1. Field of the Invention
The present invention relates to a floppy disk (flexible disk) unit frequently used as a recording medium which is light in weight and can be handled easily, and in particular, to a liner of the floppy disk unit.
2. Description of Related Art
As already known, a floppy disk unit comprises at least a cartridge case or a jacket, a flexible magnetic disk rotatably accommodated in the cartridge case or the jacket, and liners disposed on the inner surface of the cartridge case or the jacket.
Each of the above-mentioned liners is composed of a non-woven cloth having features of electrostatic elimination of a magnetic disk for removing dusts or abrasion powder, and is required to produce little lint (small quantity of fiber dust) and to have a high cleaning feature. Therefore, there have been used in general, for example, a polyethylene terephthalate fiber, an acryl fiber and so on.
In recent times, for achieving a high density recording, there is used a magnetic layer which contains ferromagnetic metal powder, for example, pure iron, cobalt, cobalt-nickel, cobalt-phosphor and so on. Since each of these magnetic metal powders has, in general, a lower hardness in comparison with a magnetic iron oxide powder such as .gamma.-Fe.sub.2 O.sub.3 or the like, the magnetic layer suffers a severe abrasion due to the sliding contact thereof with the magnetic head. For preventing this abrasion, the magnetic layer is mixed with a reinforcing powder, for example, an aluminum oxide or the like for increasing the hardness of the magnetic layer. However, when a reinforcing powder having a greater hardness is contained in the magnetic layer as mentioned above, a problem occurs that, since the above-mentioned polyethylene terephthalate fiber or the acryl fiber is weak against abrasion, the liner is abrased due to the relative sliding motion between the magnetic disk and the liner, thereby producing liner abrasion powder which may cause errors in recording and reproducing.
In view of this problem, the present assignee has offered, in Japanese Patent Application No. 63-173724 (Japanese Patent Unexamined Publication No. 2-24888), a liner, in which at least the surface layer of the liner in sliding contact with the magnetic disk is composed of a rayon cloth in consideration not only of the low lint and high cleaning feature, but also of the durability of the liner.
As mentioned-above, when at least the surface layer of the liner in sliding contact with the magnetic disk is composed of a rayon cloth, the durability of the liner is increased in comparison with that of the liner using polyethylene terephthalate (polyesther) fiber or acryl fiber, these fibers being frequently used in the past. It has been found, however, that, when the line recording density of a magnetic disk is greater than 20 KFCI (flux-change per 2.54 cm), a small amount of liner abrasion powder, which is so small as to have caused no problem in the past, becomes a cause of errors, and that the liner using a rayon fiber has insufficient durability (because minute liner abrasion powder is generated) in such a super-high density recording.